Annals of botany最新文献

Background and aims: Each branch internode, with the organs growing on it, can be seen as a single morphological phytomer subunit made of structurally and functionally interrelated components. However, allometric relationships between the anatomy and morphology of these subunits remain unclear, particularly in the axial context. The aim of this study was to address this knowledge gap by measuring morpho-anatomical parameters and their allometric relationships along grapevine shoots.

Methods: To facilitate comparison, shoot length was normalized, and a relative position index was calculated for each internode, ranging from zero at the base to one at the apex. Scaling relationships between morpho-anatomical parameters along the axis were developed and validated by statistical modelling.

Key results: Most morpho-anatomical parameters displayed an axial behaviour of increasing then decreasing in size from base to apex, with the exception of shoot diameter and shoot vessel density. A relative position index of 0.2 acted as the data turning point for most variables analysed. During the first phase (relative position index of <0.2), the traits of the phytomer organs are uncoupled and show weak allometric correlation, and during the second phase the traits exhibit strong allometric relationships.

Conclusions: Our findings suggest that allometric relationships along grapevine shoots are not constant; they exhibit a bimodal pattern, possibly influenced by seasonal temperatures. This work could aid in managing productivity shifts in agricultural and natural systems under global climate change and adds to basic knowledge of differentiation and development of growth units in plants.

Background: Since the mid-20th century, it has been argued by some that the transition from diploidy to polyploidy is an 'evolutionary dead end' in plants. Although this point has been debated ever since, multiple definitions of 'dead end' have been used in the polyploidy literature, without sufficient differentiation between alternative uses.

Scope: Here, we focus on the two most common conceptions of the dead-end hypothesis currently discussed: the 'lowering diversification' hypothesis and the 'rarely successful' hypothesis. We discuss the evidence for both hypotheses, and we use a recently developed method of inferring tip diversification rates to demonstrate tests for the effect of ploidy on diversification in Solanaceae.

Conclusions: We find that diversification rates in the family are not strongly correlated with ploidy or with the closely related trait of breeding system. We also outline recent work in the field that moves beyond the relatively simple question of whether polyploidy increases, decreases or does not significantly affect diversification rates in plants.

Background and aims: Heterotrophic plants have long been a challenge for systematists, exemplified by the base of the orchid subfamily Epidendroideae, which contains numerous mycoheterotrophic species.

Methods: Here we address the utility of organellar genomes in resolving relationships at the epidendroid base, specifically employing models of heterotachy, or lineage-specific rate variation over time. We further conduct comparative analyses of plastid genome evolution in heterotrophs and structural variation in matK.

Key results: We present the first complete plastid genomes (plastomes) of Wullschlaegelia, the sole genus of the tribe Wullschlaegelieae, revealing a highly reduced genome of 37 kb, which retains a fraction of the genes present in related autotrophs. Plastid phylogenomic analyses recovered a strongly supported clade composed exclusively of mycoheterotrophic species with long branches. We further analysed mitochondrial gene sets, which recovered similar relationships to those in other studies using nuclear data, but the placement of Wullschlaegelia remains uncertain. We conducted comparative plastome analyses among Wullschlaegelia and other heterotrophic orchids, revealing a suite of correlated substitutional and structural changes relative to autotrophic species. Lastly, we investigated evolutionary and structural variation in matK, which is retained in Wullschlaegelia and a few other 'late stage' heterotrophs and found evidence for structural conservation despite rapid substitution rates in both Wullschlaegelia and the leafless Gastrodia.

Conclusions: Our analyses reveal the limits of what the plastid genome can tell us on orchid relationships in this part of the tree, even when applying parameter-rich heterotachy models. Our study underscores the need for increased taxon sampling across all three genomes at the epidendroid base, and illustrates the need for further research on addressing heterotachy in phylogenomic analyses.

Background and aims: Fertilization relies on pollen mother cells able to transition from mitosis to meiosis to supply gametes. This process involves remarkable changes at the molecular, cellular and physiological levels, including (but not limited to) remodelling of the cell wall. During the onset of meiosis, the cellulose content in the pollen mother cell walls gradually declines, with the concurrent deposition of the polysaccharide callose in anther locules. We aim to understand the biological significance of cellulose-to-callose turnover in pollen mother cells walls.

Methods: We carried out electron microscopic, aniline blue and renaissance staining analyses of rice flowers.

Key results: Our observations indicate that in wild-type rice anthers, the mitosis-to-meiosis transition coincides with a gradual reduction in the number of cytoplasmic connections called plasmodesmata. A mutant in the Oryza sativa callose synthase GSL5 (Osgsl5-3), impaired in callose accumulation in premeiotic and meiotic anthers, displayed a greater reduction in plasmodesmata frequency among pollen mother cells and tapetal cells, suggesting a role for callose in maintenance of plasmodesmata. In addition, a significant increase in extracellular distance between pollen mother cells and impaired premeiotic cell shaping was observed in the Osgsl5-3 mutant.

Conclusions: The results suggest that callose-to-cellulose turnover during the transition from mitosis to meiosis is necessary to maintain cell-to-cell connections and optimal extracellular distance among the central anther locular cells. The findings of this study contribute to our understanding of the regulatory influence of callose metabolism during initiation of meiosis in flowering plants.

Background and aims: The master transcription factor NAC SECONDARY WALL THICKENING PROMOTING FACTOR3 (NST3), also known as SND1, plays a pivotal role in regulating secondary cell wall (SCW) development in interfascicular and xylary fibres in Arabidopsis thaliana. Despite progress in understanding SCW assembly in xylem vessel-like cells, the mechanisms behind its assembly across different cell types remain unclear. Overexpression of NST3 or its homologue NST1 leads to reduced fertility, posing challenges for studying their impact on secondary wall formation. This study aimed to develop a tightly regulated dexamethasone (DEX)-inducible expression system for NST3 and NST1 to elucidate the structure and assembly of diverse SCWs.

Methods: Using the DEX-inducible system, we characterized ectopically formed SCWs for their diverse patterns, mesoscale organization, cellulose microfibril orientation and molecular composition using spinning disc confocal microscopy, field emission scanning electron microscopy, vibrational sum-frequency generation spectroscopy, and histochemical staining and time-of-flight secondary ion mass spectrometry, respectively.

Key results: Upon DEX treatment, NST3 and NST1 transgenic hypocotyls underwent time-dependent transdifferentiation, progressing from protoxylem-like to metaxylem-like cells. NST3-induced plants exhibited normal growth but had rough secondary wall surfaces with delaminating S2 and S3 layers. Mesoscale examination of induced SCWs in epidermal cells revealed that macrofibril thickness and orientation were comparable to xylem vessels, while wall thickness resembled that of interfascicular fibres. Additionally, induced epidermal cells formed SCWs with altered cellulose and lignin contents.

Conclusions: These findings suggest NST3 and/or NST1 induce SCWs with shared characteristics of both xylem and fibre-like cells forming loosely arranged cell wall layers and cellulose organized at multiple angles relative to the cell growth axis and with varied cellulose and lignin abundance. This inducible system opens avenues to explore ectopic SCWs for bioenergy and bioproducts, offering valuable insights into SCW patterning across diverse cell types and developmental stages.

Background and aims: Poikilohydry describes the inability of plants to internally regulate their water content (hydroregulation), whereas desiccation tolerance (DT) refers to the ability to restore normal metabolic functions upon rehydration. The failure to clearly separate these two adaptations has impeded a comprehensive understanding of their unique evolutionary and ecological drivers. Unlike bryophytes and angiosperms, these adaptations in ferns are sometimes uncorrelated, offering a unique opportunity to navigate their intricate interplay.

Methods: We classified ferns into two syndromes: the Hymenophyllum-type (H-type), encompassing species with filmy leaves lacking stomata that experience extreme poikilohydry and varying degrees of DT, and the Pleopeltis-type (P-type), consisting of resurrection plants with variable hydroregulation but high DT.

Key results: The H-type evolved during globally cool Icehouse periods, as an adaptation to low light levels in damp, shady habitats, and currently prevails in wet environments. Conversely, the P-type evolved predominantly under Greenhouse periods as an adaptation to periodic water shortage, with most extant species thriving in warm, seasonally dry habitats.

Conclusions: Out study underscores the fundamental differences between poikilohydry and DT, emphasizing the imperative to meticulously differentiate and qualify the strength of each strategy as well as their interactions, as a basis for understanding the genetic and evolutionary background of these ecologically crucial adaptations.

Background and aims: Soil endemics have long fascinated botanists owing to the insights they can provide about plant ecology and evolution. Often, these species have unique foliar nutrient composition patterns that reflect potential physiological adaptations to these harsh soil types. However, understanding global nutritional patterns to unique soil types can be complicated by the influence of recent and ancient evolutionary events. Our goal was to understand whether plant specialization to unique soils is a stronger determinant of nutrient composition of plants than climate or evolutionary constraints.

Methods: We worked on gypsum soils. We analysed whole-plant nutrient composition (leaves, stems, coarse roots and fine roots) of 36 native species of gypsophilous lineages from the Chihuahuan Desert (North America) and the Iberian Peninsula (Europe) regions, including widely distributed gypsum endemics, as specialists, and narrowly distributed endemics and non-endemics, as non-specialists. We evaluated the impact of evolutionary events and soil composition on the whole-plant composition, comparing the three categories of gypsum plants.

Key results: Our findings reveal nutritional convergence of widely distributed gypsum endemics. These taxa displayed higher foliar sulphur and higher whole-plant magnesium than their non-endemic relatives, irrespective of geographical location or phylogenetic history. Sulphur and magnesium concentrations were mainly explained by non-phylogenetic variation among species related to gypsum specialization. Other nutrient concentrations were determined by more ancient evolutionary events. For example, Caryophyllales usually displayed high foliar calcium, whereas Poaceae did not. In contrast, plant concentrations of phosphorus were mainly explained by species-specific physiology not related to gypsum specialization or evolutionary constraints.

Conclusions: Plant specialization to a unique soil can strongly influence plant nutritional strategies, as we described for gypsophilous lineages. Taking a whole-plant perspective (all organs) within a phylogenetic framework has enabled us to gain a better understanding of plant adaptation to unique soils when studying taxa from distinct regions.

Background and aims: The cell walls of charophytic algae both resemble and differ from those of land plants. Cell walls in early-diverging charophytes (e.g. Klebsormidiophyceae) are particularly distinctive in ways that might enable survival in environments that are incompatible with land-plant polymers. This study therefore investigates the structure of Klebsormidium polysaccharides.

Methods: The 'pectin' fraction (defined by extractability) of Klebsormidium fluitans, solubilized by various buffers from alcohol-insoluble residues, was digested with several treatments that (partly) hydrolyse land-plant cell-wall polysaccharides. Products were analysed by gel-permeation and thin-layer chromatography.

Key results: The Klebsormidium pectic fraction made up ~30-50 % of its alcohol-insoluble residue, was optimally solubilized at pH 3-4 at 100 °C, and contained residues of xylose ≈ galactose > rhamnose > arabinose, fucose, mannose and glucose. Uronic acids were undetectable, and the pectic fraction was more readily solubilized by formate than by oxalate, suggesting a lack of chelation. Some land-plant-targeting hydrolases degraded the Klebsormidium pectic fraction: digestion by α-l-arabinanase, endo-β-(1→4)-d-xylanase and α-d-galactosidase suggests the presence of β-(1→4)-xylan with terminal α-l-arabinose, α-d-galactose and (unexpectedly) rhamnose. 'Driselase' released oligosaccharides of xylose and rhamnose (~1:1), and graded acid hydrolysis of these oligosaccharides indicated a 'rhamnoxylan' with rhamnose side-chains. Partial acid hydrolysis of Klebsormidium pectic fraction released rhamnose plus numerous oligosaccharides, one of which comprised xylose and galactose (~1:2 Gal/Xyl), suggesting a galactoxylan. Lichenase was ineffective, as were endo-β-(1→4)-d-galactanase, endo-β-(1→4)-d-mannanase, β-d-xylosidase and β-d-galactosidase.

Conclusions: Klebsormidium pectic fraction possesses many land-plant-like linkages but is unusual in lacking uronic acid residues and in containing rhamnoxylan and galactoxylan domains. Uronic acids allow land-plant and late-diverging charophyte pectins to form Ca2+-bridges, facilitating cell-wall polymer association; their absence from Klebsormidium suggests that neutral heteroxylans rely on alternative cross-linking mechanisms. This lack of dependence on Ca2+-bridges might confer on Klebsormidium the ability to grow in the acidic, metal-rich environments that it tolerates.

Background and aims: Secondary pollen presentation, the relocation of pollen from the anthers to elsewhere on the flower, has evolved multiple times across many plant families. While hypotheses suggest it evolved to promote outcrossing, a by-product of relocation may be protection of pollen from loss due to abiotic factors. In Campanulaceae pollen is presented on pollen-collecting hairs along the style and the hairs retract over time and release pollen for transfer. Campanulaceae taxa vary in the degree to which pollen is exposed to environmental factors due to variation in the corolla shape and size. We tested the protective function of pollen-collecting hairs by assessing whether there was a trade-off between the protection provided by the corolla and the pollen-collecting hairs.

Methods: We used phylogenetic comparative methods to test for associations between pollen-collecting hair length, floral shape and size metrics, and pollen exposure traits across 39 species.

Results: We anticipated longer pollen-collecting hairs in taxa with more exposed pollen presentation but found there was no relationship between estimates of pollen exposure and pollen-collecting hair length. However, pollen-collecting hair length scaled allometrically with floral size, and variation in pollen-collecting hairs, as well as most floral traits, was phylogenetically structured.

Conclusions: These results indicate that variation in pollen exposure across species does not structure variation in the pollen-collecting hairs, rather hair length scales allometrically and is phylogenetically constrained; therefore pollen-collecting hairs are unlikely to facilitate protection from environmental pressures.